Identity and year are more important than social interactions as predictors of gut microbiota in a facultatively social rodent

Abstract Social behavior is an important route by which animals can acquire their gut microbiota. Relatively few studies, however, have investigated this mechanism of microbial transfer in species lacking spatially distinct, behaviorally exclusive social groups. To determine if social behavior influences gut microbial composition and diversity in a facultatively social rodent – the California ground squirrel (Otospermophilus beecheyi) – we combined observations of social interactions with microbial characterizations of fecal samples from 98 distinct ground squirrels monitored between 2018 and 2022. We found an effect of social interactions on the similarity of individual microbial communities in only one of the five years for which data were available. No effects of social network metrics on microbial diversity were detected and there was no relationship between social group membership and microbial community composition. Instead, individual identity and year were the strongest predictors of gut microbial composition. These results suggest that social transmission of microbes may be limited in this species, with other factors (e.g., differences in individual phenotypes, seasonal shifts in diet) being potentially more important in determining the composition of the gut microbiota. Our findings emphasize the need for further study of the specific mechanisms by which social interactions may contribute to exchange of microbes and how those mechanisms vary across different social systems.